Manual wheelchair users control and propel their wheelchairs with the handrims, also commonly called pushrims, handrings, and handrails. Handrims enable the user to propel forward, turn and brake. Unfortunately, there is a high occurrence of upper extremity injuries as a result of the repetitive stresses experienced by the user when gripping and pushing their handrims.
When propelling forward, the typical wheelchair user reaches back, grips both handrims and pushes forward until their arms are almost fully extended. The user then releases the handrim and prepares for the next push if needed. Another technique sometimes used when starting from rest or climbing a steep incline is to grab both the wheel and handrim to push. Positioning the palm of the hand on the tire and wrapping the fingers around the handrim, this provides addition torque and gripping surface area than just gripping the handrim.
Breaking is done by lightly gripping the handrim as it rotates and slides through the user's hands, decelerating the rotation of the wheels. The greater the gripping force, the higher amount of friction between the hands and handrims, and ultimately the greater the deceleration. Since wheelchair users rely on their upper extremities in this manner, pain and injuries to their arms and shoulders can significantly affect their mobility, and consequently, their independence and quality of life.
The typical handrim used by the manual wheelchair population is substantially equivalent to U.S. Pat. No. 4,687,218 (issued to Okamoto on Aug. 18, 1987), which is incorporated herein in its entirety by specific reference for all purposes. This design presents a hand rim that uses rigid standoffs spanning between the wheel rim and the handrim. Machine screws fasten the handrim to the wheel rim. Another known prior art is to attach the handrim to the wheel rim by welding rigid mounting flange members to the wheel rim and handrim.
Although effective, there are some drawbacks and inconveniences that are inherent with these designs. One drawback is that these handrims have a limited gripping surface for the user's hand to engage during pushing and breaking. An increase in contact area would cause an increase in propulsion efficiency.
Another drawback is that the offset between the handrim and the wheel is not adjustable, providing a standard spanning distance for all users regardless of their hand size and gripping limitations. This makes it impossible for users with smaller hands to use the previously discussed technique of grabbing both the wheel and handrim for climbing hills or starting from rest. In addition, quad users are sometimes not provided with sufficient space to push down on the handrim because of its proximity to the wheel.
It is also known that the user's fingers can get caught in the area between the wheel and handrim or jammed by the rigid standoffs as the wheel rotates.
Another characteristic of typical handrims is that most are generally made of a smooth metal with poor frictional properties. This results in the users needing to grip on the rim with considerable force in order to prevent slippage. Some designs have used friction coatings or materials, such as vinyl or foam, to reduce slipping and minimize the needed gripping force. While these designs are effective in improving the frictional propertied of the handrim, the coating tends to burn the hand of the user during braking.
As an alternative, other handrim designs have placed high friction materials in selected locations, which provide smooth surfaces for the user to grip during braking. While these designs are better than the typical handrim, one problem they possess is that the location of the high friction is permanent. Depending on the condition of the user and their grip limitations, the proximity of the high friction with respect to the wheel rim and tire, and with respect to the handrim contour itself, should be individualized to maximize its benefits.
This leads to the need for a wheelchair manual handrim that allows users to have the ability to move the handrim and high friction material to locations that they desire. The ability to adjust these allows users to reduce the amount of gripping force needed to push, thus relieving existing pain and reducing the potential of developing repetitive stress injuries.